The need to externally process (in some way) information and convey that information to a user has been around for a long time. For example, blind persons can use canes or Seeing Eye dogs to navigate: these devices translate information that would normally be processed visually into another sense that the blind person can perceive: in this case, the sense of touch.
Military applications of data processing also exist. In the early days of air warfare, the pilot (usually the sole person in the plane, and therefore also responsible for firing the weapons) had to locate enemy planes using the senses of sight and sound. With the advent of detection apparatuses (for example, radar) that extend beyond the pilot's range of vision, the pilot has access to additional information. This information is provided to the pilot using a head's-up display.
But the information provided can often be overwhelming. Even in the early days of air travel, without the development of technologies such as radar, a pilot had a great deal of data he must process visually: visually checking the skies for their current condition; checking instruments for current elevation, the current roll, pitch, and yaw of the aircraft, the speed of the aircraft, current fuel reserves, and so on. Specialized pilots might also have to keep track of additional information: for example, a military pilot needs to know how much weaponry he is still carrying.
The use of head's up displays can reduce the number of different places a pilot has to look at to gather the information he needs. Instead of looking for a particular instrument in the cockpit, the pilot just looks at a particular location on the head's-up display. But as more and more information is conveyed to the pilot, he has to look at more places in the head's-up display to find everything he needs to know, and he has to process all the visual information to understand what the data represents.
A need remains for a way to address these and other problems associated with the prior art.